Wave soldering is a well known process for bonding leads on an electronic component to metallized areas on the bottom surface of a substrate such as a printed circuit board. Generally, wave soldering is accomplished by first applying flux to the metallized areas on the bottom surface of the circuit board and to the tip portions of the leads received in apertures in the board so as to extend below the bottom surface thereof. The flux removes oxides on the tips of the leads and on the metallized areas on the board and also serves to wet the surfaces thereof. After the leads and the metallized areas have been fluxed, the component and the printed circuit board are heated, typically by way of infrared lamps, prior to passage over a fountain of solder. In this way thermal shock to the components on the board caused by hot solder from the fountain contacting a much cooler lead thereof is avoided. The circuit board is then passed over the fountain which produces a wave of solder that flows against the bottom surface of the circuit board to bond the tip portion of the leads extending below the bottom surface of the board to the metallized areas thereon.
In the past, the process of wave soldering has, for the most part, been performed using a rosin base flux. In an effort to increase the efficiency of the wave soldering process, more chemically active water soluble fluxes have been developed for use in place of less chemically active rosin base fluxes. The increased chemical activity of water soluble fluxes enables rapid removal of any oxides on the leads and on the metallized areas on the circuit board which allows for an increased number of circuit boards to be wave soldered in a given time.
Because they are chemically very active, water soluble fluxes have been known to cause corrosion of the leads of the component. Corrosion not only occurs at the tip portion of the lead where the flux is applied, but along the entire length of the lead as well. Such corrosion results from the upward migration along the lead of corrosive flux vapors produced when the flux, which coats the tips of the leads, is heated. Should the corrosion on the lead actually penetrate the component, then component failure may occur.
Accordingly, there is a need for a technique for reducing the likelihood of component failure caused by the use of corrosive fluxes during wave soldering.